1. Field of the Invention
The present invention generally relates to a data recording device, a data reproducing and a data recording medium. More particularly, the present invention relates to techniques for easily and reliably managing a plurality of recording media or the like, on which divided image data are respectively recorded, even in the case that data compression rate largely varies with the contents of the data, and for recording mass image data, whose picture quality is effectively prevented from being degraded, by recording image data after securing a region according to the preliminarily estimated number of recording media or information recording surfaces at the time of recording image data by using, for example, MPEG (Moving Picture Experts Group) system, and by recording management data on this region according to the recorded image data.
2. Description of the Related Art
Hitherto, in the case of recording image data on an optical disk or the like, the image data is encoded before recorded. Further, a coding method using MPEG has been proposed as this technique for encoding image data.
Namely, this MPEG system first performs a discrete cosine transform (DCT) on image data prescribed by a predetermined color difference format (for instance, 4:2:2) in DCT blocks. Thereafter, this MPEG system encodes the image data sequentially by utilizing the correlation between coefficient data obtained as a result of the DCT and by transforming one or more coefficient data into a single variable-length code. At that time, MPEG system assigns a variable-length code, whose data length varies with the frequency (or incidence) of the coefficient data, to the image data. Thereby, the data compression rate is greatly enhanced in comparison with conventional coding systems. Ccnsequently, the image data (namely, the coefficient data) can be efficiently transmitted.
Further, MPEG system is defined in such a manner that before such a process, the quantity of data is reduced by effectively utilizing the correlation between consecutive image data through inter-frame coding and intra-frame coding performed thereon. Thereby, the data compression rate can be further enhanced.
Namely, this DCT block consists of image data of 8.times.8 pixels. Further, MPEG system performs the coding in DCT blocks. Moreover, a macroblock is defined as being composed of four DCT blocks represented by luminance signals (namely, four DCT blocks, each of which consists of image data of 8.times.8 pixels represented by luminance signals) and DCT blocks represented by color difference signals corresponding to the four DCT blocks represented by luminance signals. Furthermore, in MPEG system, a slice is defined as a set of macroblocks. Additionally, a GOP (namely, Group Of Pictures) is defined as a set of the slices. Besides, a sequence corresponding to image data, which represent (a sheet of) an image, is defined as a set of GOPs.
Thus, in MPEG system, data structure is defined as a hierarchial structure having six layers, namely, a sequence layer consisting of sequences, a GOP layer consisting of GOPs (Group Of Pictures), a picture layer consisting of pictures, a slice layer consisting of slices, a macroblock layer consisting of macroblocks and a block layer consisting of blocks, which are serially arranged in descending order. Among these layers, the sequence layer and the GOP layer of high orders are determined as illustrated in FIG. 15(A) and 15(B).
Namely, the sequence layer corresponds to image data of a sheet of an image. In the case of recording image data on an optical disk of such a type, MPEG system performs a sequence control operation in such a way that information of this sequence layer is continuously allocated (or located). First, a sequence header code (SHC) designating the beginning of the sequence layer is allocated. Next, information of the sequence layer, which represents the number of pixels of an image and the aspect ratio thereof and so on, is continuously allocated as illustrated in FIG. 15(A). Subsequently, information of GOP layer (of the sequence layer) is iteratively allocated a predetermined number of times. Then, such information is followed by other information of the sequence layer, namely, SEC (Sequence End Code) is allocated.
Further, regarding GOP layer, this layer is the smallest unit of a screen (or scene) group which is a unit to be accessed randomly. First, GSC (Group Start Code) representing the beginning of GOP is allocated. Then, TC (Time Code) representing a time period having passed since the beginning of the sequence is further allocated. Subsequently, information concerning predetermined flags or the like is allocated. Thereafter, information of the picture layer is allocated iteratively. Thus, GOP layer is formed as illustrated in FIG. 15(B).
Moreover, as to the picture layer, after SHC and information concerning a motion vector or the like are serially allocated, information of the slice layer is iteratively allocated a predetermined number of times. Thus the picture layer is formed. Similarly, the slice layer is formed by after SHC and so forth are allocated. Furthermore, in the case of the macroblock layer, necessary information is allocated in DCT blocks, and a variable-length code as previously described is repeated as the DCT block.
Additionally, the inter-frame coding and the intra-frame coding are distinguished from each other according to a closed GOP flag, which is allocated subsequent to a time code TC in the GOP layer and indicating whether or not GOP is reproduced independently of other GOPs. MPEG standard defines two types of pictures obtained by performing the inter-frame coding, namely, P-Pictures (Predictive Pictures), on which the inter-frame coding is performed with respect to previously transmitted image data, and B-Pictures (Bidirectionally predictive Pictures), on which the inter-frame coding is performed with respect to both of precedent and subsequent image data.
Meanwhile, in the case of MPEG transform algorithm, when performing the variable-length coding on coefficient data, the variable-length coding is conducted after the quantization of this coefficient data is carried out according to a predetermined quantization table. Incidentally, the data compression rate can be changed by switching this quantization table to another quantization table.
Thereby, even in the case that it is difficult to record a single program on a single optical disk by performing an ordinary process, MPEG system can record mass image data on this single optical disk by changing the quantization table to another quantization table employing a coarse quantization size. However, when enhancing the data compression rate in this way, there is caused a problem that the picture quality is degraded.
As a method for solving such a problem, there has been contrived, for example, a method of splitting (namely, dividing) and recording a program across a plurality of optical disks, when it is difficult to record a single program on a single optical disk. However, in the case that a single program is split (and recorded) across a plurality of optical disks, respectively, there is caused a problem that the management of the plurality of optical disks is troublesome in a playback (or reproduction) unit. Further, there is the fear that special playbacks such as a random access playback becomes difficult.
Especially, the coding systems such as MPEG system have characteristics that the final quantity of whole data varies largely according to picture properties as a result of performing the inter-frame coding, by which the quantity of data is reduced by utilizing the correlation between image data, and performing DCT process and the variable-length coding. Therefore, even when starting the recording by preliminarily intending to record image data on a plurality of optical disks, the number of optical disks, on which image data is actually recorded, is sometimes different from the estimated number of optical disks. Consequently, there is a problem that it is difficult to preliminarily prepare management data for managing the plurality of optical disks.
Further, when using the coding systems such as MPEG system, in the case of simply splitting and recording a program at a predetermined time across a plurality of optical disks by iteratively performing the inter-frame coding and the intra-frame coding, there is the fear that immediately after changing one of the optical disks to another thereof, the image cannot be reproduced.
The present invention is accomplished in view of the aforementioned problems.
It is, accordingly, an object of the present invention to propose a data recording device, a data playback (or reproducing) device and a data recording medium, by which mass data representing images can be recorded and reproduced easily and reliably by effectively preventing the picture quality from being degraded, at the time of recording image data by using, for example, MPEG system.